Being able to visualize blood flow in live tissue may aid with medical diagnoses or medical procedures, including surgical procedures. Imaging techniques may be sensitive enough to identify areas of blood flow near the surface of tissue without significant processing of the image data. However, blood vessels are not always near the surface of a tissue and not always easily imaged. Blood that flows deeper in a tissue may be more difficult to detect in an image. For blood vessels located far below the tissue surface, the image signal from the blood vessel may be low. Materials nearer the surface, including skin and bone, may obscure any signal from a blood vessel underneath those materials. As a result, image characteristics related to the flow of blood, such as blurring or low contrast, may be difficult to identify in an unprocessed image. Improved methods and systems of detecting flow in images are desired. These and other needs are addressed.